Polymeric fibers have been known essentially since the beginnings of commercial polymer development. The production of polymer fibers from polymer films is also well known. In particular, the ease with which films produce fibers (i.e., fibrillate) can be correlated to the degree of molecular orientation of the polymer fibrils that make up the film.
Orientation of crystalline polymeric films and fibers has been accomplished in numerous ways, including melt spinning, melt transformation (co)extrusion, solid state coextrusion, gel drawing, solid state rolling, die drawing, solid state drawing, and roll-trusion, among others. Each of these methods has been successful in preparing oriented, high modulus polymer fibers and films. Most solid-state processing methods have been limited to slow production rates, on the order of a few cm/min. Methods involving gel drawing can be fast, but require additional solvent-handling steps. A combination of rolling and drawing solid polymer sheets, particularly polyolefin sheets, has been described in which a polymer billet is deformed biaxially in a two-roll calender then additionally drawn in length (i. e., the machine direction). Methods that relate to other web handling equipment have been used to achieve molecular orientation, including an initial nip or calender step followed by stretching in both the machine direction or transversely to the film length.
Liberating fibers from oriented, high-modulus polymer films, particularly from high molecular weight crystalline films, has been accomplished in numerous ways, including abrasion, mechanical plucking by rapidly-rotating wire wheels, impinging water-jets to shred or slit the film, and application of ultrasonic energy. Water jets have been used extensively to cut films into flat, wide continuous longitudinal fibers for strapping or reinforcing uses. Ultrasonic treatment of oriented polyethylene film in bulk (that is, a roll of film immersed in a fluid, subjected to ultrasonic treatment for a period of hours) has been shown to produce small amounts of microfibrils.